Mi vecina anda diciendo que la grieta del rellano es más grande.

Because vecina is the feminine form of vecino.

• vecino = male neighbour / neighbour in general in some contexts
• vecina = female neighbour

So Mi vecina means my female neighbour.

The possessive mi does not change for gender here:

• mi vecino
• mi vecina

Andar + gerund is a common Spanish structure. Here, anda diciendo means something like:

• has been going around saying
• keeps saying
• is saying around
• has been saying

It often suggests that the person is saying something repeatedly, informally, or to different people.

So this is not just a neutral she is saying. It can sound more like she’s been going around saying...

Good question. Both are possible, but they do not feel the same.

• está diciendo = she is saying, right now / at this moment
• anda diciendo = she has been going around saying, keeps saying, is saying in a way that feels more repeated or spread around

In many contexts, andar + gerund adds a nuance of:

• repetition
• movement from place to place or person to person
• mild criticism, annoyance, or gossip

So Mi vecina anda diciendo que... can sound a bit like: My neighbour is going around saying that...

Often, yes.

It very often suggests that the speaker is not completely neutral about it. It can imply:

• the neighbour keeps bringing it up
• the neighbour is gossiping
• the speaker is slightly annoyed
• the speaker may doubt or dislike what she is saying

That said, the exact tone depends on context and intonation. But in everyday Spanish, andar diciendo frequently carries that extra flavour.

Here que introduces a subordinate clause: what the neighbour is saying.

Structure:

• Mi vecina anda diciendo = My neighbour has been going around saying
• que la grieta del rellano es más grande = that the crack on the landing is bigger

So que here means that.

In English, that is often optional:

• My neighbour keeps saying that the crack...
• My neighbour keeps saying the crack...

In Spanish, que is normally required here.

• grieta = crack, split, fissure in a wall, floor, ceiling, etc.
• rellano in Spain usually means a landing, especially the shared area at the top of stairs or outside flats in an apartment building

So la grieta del rellano means:

• the crack in/on the landing
• the crack on the apartment landing

In Spain, rellano is a very normal word in building-related contexts.

Because de + el contracts to del.

So:

• de + el = del
• a + el = al

Examples:

• la puerta del piso = the door of the flat
• la grieta del rellano = the crack of/on the landing

This contraction is mandatory with el, unless el is part of a proper name.

Because ser is normally used for describing an inherent or identifying characteristic, while estar is usually for states or conditions.

Here, the sentence treats the crack’s size as a characteristic:

• La grieta es más grande = The crack is bigger

Spanish usually uses ser with size:

• Es grande
• Es pequeña
• Es más grande

Using estar grande is much less normal here. For physical size, ser is the expected choice.

Yes. In this sentence, más grande means bigger or larger.

• grande = big / large
• más grande = bigger / larger

Spanish often uses más + adjective for comparisons:

• más grande = bigger
• más pequeño = smaller
• más alto = taller
• más caro = more expensive

So la grieta ... es más grande = the crack ... is bigger.

Spanish, like English, can leave the second part of the comparison understood from context.

So es más grande can mean:

• bigger than before
• bigger than my neighbour thought
• bigger than another crack
• simply getting bigger, depending on context

If Spanish wants to state the comparison explicitly, it can:

• es más grande que antes = it’s bigger than before
• es más grande que la otra = it’s bigger than the other one

Here, the sentence leaves that unsaid because the context probably makes it obvious.

Because Spanish often omits subject pronouns when the verb ending already shows who the subject is.

• ando = I go around / I am going around
• andas = you go around
• anda = he/she/it goes around / is going around

So Mi vecina anda diciendo... already clearly tells us the subject:

• mi vecina = the subject noun
• anda agrees with that subject

You could say Ella anda diciendo..., but here it would be unnecessary unless you wanted extra emphasis or contrast.

Yes, but the meaning would be flatter and more neutral.

Compare:

• Mi vecina dice que la grieta del rellano es más grande.
  = My neighbour says the crack on the landing is bigger.

• Mi vecina anda diciendo que la grieta del rellano es más grande.
  = My neighbour has been going around saying / keeps saying that the crack on the landing is bigger.

So dice reports the fact more neutrally.
anda diciendo adds the idea of repetition and often a slightly gossipy or annoyed tone.

It is a periphrastic verbal expression: a conjugated verb plus a gerund.

Here:

• anda = present tense of andar
• diciendo = gerund of decir

So the pattern is:

andar + gerund

Examples:

• anda buscando trabajo = he/she is going around looking for work
• andan hablando de ti = they’ve been going around talking about you
• anda diciendo tonterías = he/she keeps saying nonsense

The gerund of decir is irregular:

• decir → diciendo

It is very common in Spain, especially for the landing in a block of flats or a staircase.

In other Spanish-speaking regions, people may still understand it, but other words may be more common depending on the country and the exact part of the building.

So for Spanish from Spain, rellano is a very natural choice here.